First off, Shetlands do not get their tails banded. They are a Northern Shorttailed breed and cannot be registered if the tails have been ringed. For testicles, with this breed you are unlikely to be able to get a ring on for the first few days as they are small in that department.
As Sally says, Shetlands very rarely need assistance, and are best left to get on with it in peace, with you keeping an eye on them from a discreet distance. Don't fuss them and they will know what to do especially if they have lambed before.
My best advice is to know beforehand what a normal, unassisted birth looks like so you have an idea of timings, how much effort the ewe will exert, how to clear the lamb's airway with your fingers if it doesn't lift its head promptly.
For the births themselves, you need 10% iodine in a mint sauce type jar, old towels, baby wipes, disposable gloves and self confidence. Lambing ropes, spoons and so on are not something you are likely ever to need, and you can get an emergency vet out at any time of day or night if it goes wrong. We also have a long acting Penicillin available, but again if you don't know when to use it you would have a vet there anyway.